The present invention relates to cryosurgical systems and methods useable for planning and for facilitating a cryoablation procedure. More particularly, the present invention relates to the use of integrated images displaying, in a common virtual space, images of a three-dimensional model of a surgical intervention site, simulation images of a planned cryoablation procedure at the site, and real-time images of the site during cryoablation. The present invention further relates to system-supplied recommendations for, and evaluations of, a planned cryoablation procedure, and to system-supplied feedback to an operator and system-supplied control signals to a cryosurgery tool during cryoablation.
Cryosurgical procedures involve deep tissue freezing which results in tissue destruction due to rupture of cells and or cell organelles within the tissue. Deep tissue freezing is effected by insertion of a tip of a cryosurgical device into the tissue, either transperineally, endoscopically or laparoscopically, and a formation of, what is known in the art as, an ice-ball around the tip.
In order to effectively destroy a tissue by such an ice-ball, the diameter of the ball should be substantially larger than the region of the tissue to be treated, which constraint derives from the specific profile of temperature distribution across the ice-ball.
Specifically, the temperature required for effectively destroying a tissue is about −40° C., or cooler. However, the temperature at the surface of the ice-ball is 0° C. The temperature declines exponentially towards the center of the ball such that an isothermal surface of about −40° C. is typically located within the ice-ball substantially at the half way between the center of the ball and its surface.
Thus, in order to effectively destroy a tissue there is a need to locate the isothermal surface of −40° C. at the periphery of the treated tissue, thereby exposing adjacent, usually healthy, tissues to the external portions of the ice-ball. The application of temperatures of between about −40° C. and 0° C. to such healthy tissues usually causes substantial damage thereto, which damage may result in temporary or permanent impairment of functional organs.
In addition, when the adjacent tissues are present at opposite borders with respect to the freeze treated tissue, such as in the case of prostate freeze treatments, as is further detailed below, and since the growth of the ice-ball is in substantially similar rate in all directions toward its periphery, if the tip of the cryosurgical device is not precisely centered, the ice-ball reaches one of the borders before it reaches the other border, and decision making of whether to continue the process of freezing, risking a damage to close healthy tissues, or to halt the process of freezing, risking a non-complete destruction of the treated tissue, must be made.
Although the present invention is applicable to any cryosurgical treatment, discussion is hereinafter primarily focused on a cryosurgical treatment of a patient's prostate.
Thus, when treating a tumor located at a patient's prostate, there is a trade-of between two options: (a) effectively destroying the prostatic tissue extending between the prostatic urethra and the periphery of the prostate and causing unavoidable damage to the patient's urethra or organs adjacent the prostate such as the rectum and nerves; (b) avoiding the damaging of the prostatic urethra and adjacent organs, but exposing the patient to the risk of malignancy due to ineffective destruction of the prostate tumor. Treatment of benign prostate hyperplasia (BPH), while not requiring total destruction of an entire volume of prostate tissue as does treatment of a malignancy, nevertheless does run the risk of causing damage to healthy functional tissues and organs adjacent to the prostate, if care is not taken to limit the scope of destructive freezing to appropriate locations.
A classical cryosurgery procedure for treating the prostate includes the introduction of 5-7 probes into the prostate, the probes being typically arranged around the prostatic urethra such that a single probe is located, preferably centered, between the prostatic urethra and the periphery of the prostate. The dimensions of such a single-probe are usually adapted for effectively treating the prostatic tissue segment extending from the urethra to the periphery of the prostate, e.g., a tip of 3 millimeters in diameter, generating an ice-ball of 3-4 centimeters in diameter, depending on the size of the prostate. Since a single ice-ball is used for freezing such a prostatic tissue segment, the volume of adjacent tissues exposed to damage is substantially greater than the volume of the treated tissue. For example, if the area of the ice-ball in cross section is πR2, and an effective treatment of at least −40° C. is provided to an area of π(R/2)2 (in cross section), then the area of adjacent tissues (in cross section) exposed to between about −40° C. and about 0° C. is πR2−0.25(πR2)=0.75(πR2), which is three times the area of the tissue effectively treated by the ice-ball.
A modification of the classic cryosurgery procedure described in the preceding paragraph, intended to avoid excessive damage to adjacent tissues, is to use such a single probe of a smaller diameter producing an ice-ball of smaller size. Such a modification, however, exposes the patient to the danger of malignancy because of a possible incomplete destruction of the tumor.
The classical cryosurgery procedure herein described, therefore, does not provide effective resolution of treatment along the planes perpendicular to the axis of penetration of the cryosurgical probe into the patient's organ.
A further limitation of the classical procedure stems from the fact that anatomical organs such as the prostate usually feature an asymmetric three-dimensional shape. Consequently, introduction of a cryosurgical probe along a specific path of penetration within the organ may provide effective treatment to specific regions located at specific depths of penetration but at the same time may severely damage other portions of the organ located at other depths of penetration.
U.S. Pat. No. 6,142,991 to Schatzberger teaches a high resolution cryosurgical method and device for treating a patient's prostate designed to overcome the described limitations of the classical cryosurgery procedure described hereinabove. Schatzberger's “high resolution” method (referred to as the “HR method” hereinbelow) comprises the steps of (a) introducing a plurality of cryosurgical probes to the prostate, the probes having a substantially small diameter and are distributed across the prostate, so as to form an outer arrangement of probes adjacent the periphery of the prostate and an inner arrangement of probes adjacent the prostatic urethra; and (b) producing an ice-ball at the end of each of said cryosurgical probes, so as to locally freeze a tissue segment of the prostate. Schatzberger's apparatus (referred to hereinbelow as the “HR” apparatus) comprises (a) a plurality of cryosurgical probes of small diameter, the probes serve for insertion into the patient's organ, the probes being for producing ice-balls for locally freezing selected portions of the organ; (b) a guiding element including a net of apertures for inserting the cryosurgical probes therethrough; and (c) an imaging device for providing a set of images, the images being for providing information on specific planes located at specific depths within the organ, each of said images including a net of marks being correlated to the net of apertures of the guiding element, wherein the marks represent the locations of ice-balls which may be formed by the cryosurgical probes when introduced through said apertures of the guiding element to said distinct depths within the organ.
The HR method and device provide the advantages of high resolution of treatment along the axis of penetration of the cryosurgical probe into the patient's organ as well as along the planes perpendicular to the axis of penetration, thereby enabling to effectively destroy selective portions of a patient's tissue while minimizing damage to adjacent tissues and organs, and to selectively treat various portions of the tissue located at different depths of the organ, thereby effectively freezing selected portions of the tissue while avoiding the damaging of other tissues and organs located at other depth along the axis of penetration.
Schatzberger, in U.S. Pat. No. 6,142,991 also teaches the additional step of three dimensionally mapping an organ of a patient so as to form a three dimensional grid thereof, and applying a multi-probe system introduced into the organ according to the grid, so as to enable systematic high-resolution three dimensional cryosurgical treatment of the organ and selective destruction of the treated tissue with minimal damage to surrounding, healthy, tissues.
It is, however, a disadvantage of the HR apparatus and method as taught in U.S. Pat. No. 6,142,991 that the apparatus enables, and the method requires, a high level of diagnostic sophistication in the selection and definition of the particular volume of tissue to be cryoablated. Real-time imaging capabilities of the HR apparatus provide for imaging of the target organ at a selected depth of penetration and thereby assist an operator in deciding where to introduce and utilize a plurality of cryogenic probes, yet the complex three-dimensional geometry of the cryoablation target is poorly rendered by the set of two dimensional images constituting the three dimensional grid as contemplated by the HR method and apparatus. In this prior art method, little assistance is provided for an operator in understanding the three dimensional shape and structure of the cryoablation target and the surrounding tissues. Information vital to the operator may be present in the set of images, yet difficult for the operator to see and appreciate. In a set of images of this type, the details may be present, yet it may be difficult to appreciate their significance because of the difficulty of seeing them in context. A three dimensional “grid” composed of a plurality of two dimensional images such as ultrasound images contain many details, yet do not facilitate the understanding of those details in a three dimensional context.
Thus there is a widely recognized need for, and it would be highly advantageous to have, an apparatus for facilitating cryosurgery which provides real-time imaging of a cryoablation target site in a manner which is easy for an operator to visualize and to understand.
It is an additional limitation of the HR method and apparatus, and of other prior art systems, that the imaging capabilities contemplated are not well adapted to assist an operator in planning a cryoablation procedure. In addition to the fact that the imaging facilities there provided are poorly adapted to visualization of the three dimensional space by an operator, they are also limited in that the apparatus is poorly adapted to providing images of the target area in advance of the operation, e.g., for planning purposes. The described HR equipment might, of course, but used to create the described three dimensional mapping of the target area well in advance of a surgical intervention, but no mechanism is provided for facilitating the relating the images so obtained, and any planned procedures based on those images, to a subsequent intervention procedure. Moreover, the fact that the imaging modality of the HR apparatus is physically connected to parts of the cryosurgery equipment limits its versatility and may in some cases make it awkward to use for creating preparatory images of an intervention site.
Thus there is a widely recognized need for, and it would be highly advantageous to have, an apparatus for planning and for facilitating cryosurgery which provides easily understandable visualization of a cryoablation target site in advance of a surgical intervention, which further provides facilities for studying the site and for planning the intervention, and which yet further provides facilities for applying information gleaned from prior study of the imaged site, and specific plans for intervening in the site, to the actual site, in real time, during the planned cryoablation operation.
It is a further limitation of the HR method that no means are provided for facilitating the relating of images obtained in advance of a surgical intervention to a subsequent intervention. Yet whereas ultrasound images of a target site can be generated in real time during an intervention, and MRI techniques may also (if somewhat less easily) also be obtained during cryosurgery, other imaging techniques (CT scans, for example) are less well adapted to being produced during the course of an actual cryosurgery intervention.
Thus there is a widely recognized need for, and it would be highly advantageous to have, an apparatus and method for facilitating the relating of images obtained prior surgery to real-time images, from the same or from additional sources, obtained during cryosurgery.
Much is now known about the tissue-destructive processes of cryoablation, and about the subsequent short-term and long-term consequences to an organ such as a prostate which has undergone partial cryoablation. The laws of physics relating to the conduction of heat in a body, reinforced by experimentation and further reinforced by accumulated clinical experience in cryosurgery, provide a wealth of information enabling to predict with some accuracy the effect of a specific planned cryoablation procedure on target tissues. This information, and this capability for prediction, is underutilized in current cryosurgery practice.
The Seednet Training And Planning Software (“STPS”) marketed by Galil Medical Ltd. of Yokneam, Israel constitutes a set in this direction, in that it provides a system for displaying, and allowing an operator to manipulate, a three-dimensional model of a prostate, and further allows an operator to plan a cryoablation intervention and to visualize the predicted effect of that planned intervention on the prostate tissues. STPS, however, is limited in that it does not provide means for relating a preliminary three dimensional model of a prostate to the prostate as revealed in real-time during the course of a surgical procedure. Moreover, the predictive ability of the STPS system is limited to predicting the extent of the freezing produced by a given deployment of a plurality of cryoprobes over a given time. No assistance is provided to an operator in discerning interactions between the predicted cryoablation and specific structures desired to be protected or to be destroyed. No assistance is given in predicting long-term effects of a given cryoablation procedure. No assistance is given in recommending procedures, placement of probes, temperature, or timing of an intervention.
Thus there is a widely recognized need for, and it would be highly advantageous to have, apparatus and method for calculating probable immediate, short-term, and long-term effects of a planned cryoablation procedure, thereby to facilitate the planning of such a procedure. There is further a widely recognized need for, and it would be highly advantageous to have, apparatus and method for facilitating the implementation of such a planned procedure, in real time, during execution of a planned cryoablation.
It is noted that with respect to BPH, the need for such a planning and facilitation apparatus is particularly strong.
BPH, which affects a large number of adult men, is a non-cancerous enlargement of the prostate. BPH frequently results in a gradual squeezing of the portion of the urethra which traverses the prostate, also known as the prostatic urethra. This causes patients to experience a frequent urge to urinate because of incomplete emptying of the bladder and a burning sensation or similar discomfort during urination. The obstruction of urinary flow can also lead to a general lack of control over urination, including difficulty initiating urination when desired, as well as difficulty in preventing urinary flow because of the residual volume of urine in the bladder, a condition known as urinary incontinence. Left untreated, the obstruction caused by BPH can lead to acute urinary retention (complete inability to urinate), serious urinary tract infections and permanent bladder and kidney damage.
Most males will eventually suffer from BPH. The incidence of BPH for men in their fifties is approximately 50% and rises to approximately 80% by the age of 80. The general aging of the United States population, as well as increasing life expectancies, is anticipated to contribute to the continued growth in the number of BPH sufferers.
Patients diagnosed with BPH generally have several options for treatment: watchful waiting, drug therapy, surgical intervention, including transurethral resection of the prostate (TURP), laser assisted prostatectomy and new less invasive thermal therapies.
Various disadvantages of existing therapies have limited the number of patients suffering from BPH who are actually treated. In 1999, the number of patients actually treated by surgical approaches was estimated to be 2% to 3%. Treatment is generally reserved for patients with intolerable symptoms or those with significant potential symptoms if treatment is withheld. A large number of the BPH patients delay discussing their symptoms or elect “watchful waiting” to see if the condition remains tolerable.
Thus, development of a less invasive, more convenient, or more successful treatment for BPH could result in a substantial increase in the number of BPH patients who elect to receive interventional therapy.
Cryoablation is a candidate for being such a popularize treatment.
With respect to drug therapies: some drugs are designed to shrink the prostate by inhibiting or slowing the growth of prostate cells. Other drugs are designed to relax the muscles in the prostate and bladder neck to relieve urethral obstruction. Current drug therapy generally requires daily administration for the duration of the patient's life.
With respect to surgical interventions: the most common surgical procedure, transurethral resection of the prostate (TURP), involves the removal of the prostate's core in order to reduce pressure on the urethra. TURP is performed by introducing an electrosurgical cutting loop through a cystoscope into the urethra and “chipping out” both the prostatic urethra and surrounding prostate tissue up to the surgical capsule, thereby completely clearing the obstruction. It will be appreciated that this procedure results in a substantial damage inflicted upon the prostatic urethra.
With respect to laser ablation of the prostate: laser assisted prostatectomy includes two similar procedures, visual laser ablation of the prostate (V-LAP) and contact laser ablation of the prostate (C-LAP), in which a laser fiber catheter is guided through a cystoscope and used to ablate and coagulate the prostatic urethra and prostatic tissue. Typically, the procedure is performed in the hospital under either general or spinal anesthesia, and an overnight hospital stay is required. In V-LAP, the burnt prostatic tissue then necroses, or dies and over four to twelve weeks is sloughed off during urination. In C-LAP, the prostatic and urethral tissue is burned on contact and vaporized. Again, it will be appreciated that these procedures result in a substantial damage inflicted upon the prostatic urethra.
With respect to heat ablation therapies: these therapies, under development or practice, are non-surgical, catheter based therapies that use thermal energy to preferentially heat diseased areas of the prostate to a temperature sufficient to cause cell death. Thermal energy forms being utilized include microwave, radio frequency (RF) and high frequency ultrasound energy (HIFU). Both microwave and RF therapy systems are currently being marketed worldwide. Heat ablation techniques, however, burn the tissue, causing irreversible damage to peripheral tissue due to protein denaturation, and destruction of nerves and blood vessels. Furthermore, heat generation causes secretion of substances from the tissue which may endanger the surrounding area.
With respect to transurethral RF therapy: transurethral needle ablation (TUNA) heats and destroys enlarged prostate tissue by sending radio waves through needles urethrally positioned in the prostate gland. The procedures prolongs about 35 to 45 minutes and may be performed as an outpatient procedure. However TUNA is less effective than traditional surgery in reducing symptoms and improving urine flow. TUNA also burn the tissue, causing irreversible damage to peripheral tissue due to protein denaturation, and destruction of nerves and blood vessels. Furthermore, as already discussed above, heat generation causes secretion of substances from the tissue which may endanger the surrounding area.
In contrast to the alternative treatments for BPH listed above, cryoablation therapy presents significant advantages. The volume of an enlarged prostate can be reduced, and stricture to the urethra can be eliminated, by selective destruction of prostate tissue by cryoablation. Tissues destroyed by cryoablation in treating BPH are gradually absorbed by the body, rather than being sloughed off during urination.
When the tissues to be cryoablated are appropriately selected and accurately cryoablated, there may be minimal endangerment of vital healthy functional tissues in proximity to the prostate. Thus, cryoablation is an important technique for treating BPH and has potential for becoming an increasingly popular therapy and enabling treatment of a large population of sufferers who today receive no effective treatment at all for their condition.
Thus, there is a widely recognized need for, and it would be highly advantageous to have, apparatus and method facilitating the planning cryoablation for the treatment of BPH by recommending appropriate number or placement of loci for cryoablation based on a patient's symptomatology, thereby helping to make this useful therapy accessible to surgeons not specialized in this specific method of treatment.
Particularly for surgeons who are not specialists in the particular limited field of cryoablation of the prostate, there is a widely recognized need for, and it would be highly advantageous to have, apparatus and method which facilitates the execution of a planned cryoablation treatment of the prostate or of another organ by providing feedback on the progress of an intervention by comparing real-time imaging of the intervention site with a planning model of the site, providing warnings when freezing, visible in ultrasound, approaches areas designated as needing to be protected from damage, or when destruction of tissues risks failing to cover volumes designated as requiring to be destroyed. Similarly, there is a widely recognized need for, and it would be highly advantageous to have, mechanisms for guiding movements of an operator during a cryoablation procedure, or for automatically managing the movement of cryosurgical tools such as cryoprobes during a cryoablation intervention, according to information based on a plan of the intervention and feedback obtained through real-time imaging of the intervention site.
In one respect, a system for planning a cryoablation intervention is particularly useful. Prior art has given little consideration to the interactive effects of a plurality of closely placed cryoprobes. Yet tissues which are in proximity to two or more cryoprobes may be cooled by several sources simultaneously, and consequently achieve a lower temperature than would be expected when considering the well-known freezing patterns created by a single cryoprobe used in isolation.
Thus there is a widely recognized need for, and it would be highly advantageous to have, system and method for utilizing a plurality of cryoprobes that takes into account their mutually-reinforcing cooling effect to create a near-uniform cold field within a volume. It would further be advantageous to have a system and method for defining a volume in which cognizance is take of the mutually reinforcing cooling effect of a plurality of closely placed cryoprobes to smoothly and accurately define a border of a cryoablation volume, thereby ensuring total destruction of tissues within that volume while minimizing damage to tissues outside that volume.